title: Translational symmetry breaking and gapping of heavy-quasiparticle pocket in URu₂Si₂.
abstract: URu₂Si₂ is a uranium compound that exhibits a so-called 'hidden-order' transition at ~17.5 K. However, the order parameter of this second-order transition as well as many of its microscopic properties remain unclarified despite considerable research. One of the key questions in this regard concerns the type of spontaneous symmetry breaking occurring at the transition; although rotational symmetry breaking has been detected, it is not clear whether another type of symmetry breaking also occurs. Another key question concerns the property of Fermi-surface gapping in the momentum space. Here we address these key questions by a momentum-dependent observation of electronic states at the transition employing ultrahigh-resolution three-dimensional angle-resolved photoemission spectroscopy. Our results provide compelling evidence of the spontaneous breaking of the lattice's translational symmetry and particle-hole asymmetric gapping of a heavy quasiparticle pocket at the transition.
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan.
authors.forename: Rikiya
authors.initials: R
authors.lastname: Yoshida
authors.forename: Koji
authors.initials: K
authors.lastname: Tsubota
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Ishiga
authors.forename: Masanori
authors.initials: M
authors.lastname: Sunagawa
authors.forename: Jyunki
authors.initials: J
authors.lastname: Sonoyama
authors.forename: Dai
authors.initials: D
authors.lastname: Aoki
authors.forename: Jacques
authors.initials: J
authors.lastname: Flouquet
authors.forename: Takanori
authors.initials: T
authors.lastname: Wakita
authors.forename: Yuji
authors.initials: Y
authors.lastname: Muraoka
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Yokoya